1) Distinct biochemical differences have been found between models for early onset retinal degeneration that were previously thought to belong to a single disease type. Although cyclic nucleotide metabolism is deranged in each animal model, quantitative and qualitative differences are observed in enzymes involved in regulating the concentration of both cAMP and cGMP. This indicates that there may be multiple etiologies of these diseases and that the causes of each disease must be separately established for each animal species or genetic variation. 2) The role of cyclic nucleotides in visual cells other than the photoreceptor visual process appears to be complex having some similarities to well known brain fractions but also some distinct and potentially unique differences. cAMP in particular appears to be involved in retinomotor movements in retina and pigment epithelium.